The present invention relates generally to a method of representing graphic data on an output device, and more particularly, to a method of generating a printed graph or chart using text characters to facilitate faster printing on non-scalable raster image printers.
It is well known in the art to print complex graphics using bit-mapping techniques. In such applications, a representation of an image to be printed is generated in a page description language (PDL) such as Postscript. The PDL defines commands which enable complete and precise control of bitmap images as well as the attributes of character fonts, including point size, orientation, shading, etc. Typically, such printers include a processor adapted for receiving the PDL instructions from a connected computer, where the printer then locally bitmaps a desired custom image on a printing medium. Although this method is capable of producing high quality graphics, it is not well suited to applications where large amounts of relatively simple graphical data are to be printed. For example, it is often necessary to print appreciable numbers of individually customized charts or the like in connection with investment reports. In such applications, the bit-mapping technique is time-consuming and inefficient, as it may be necessary to use anywhere from 10,000 to 15,000 characters to construct each image.
It is also well-known in the art to print text characters in various shapes and sizes in what is typically referred to as "text mode." Characters are grouped together as fonts having particular attributes such as point size, orientation, shading and the like. Fonts that are printable in text mode are classified as either "hard fonts" or "soft fonts." Hard fonts are comprised of predefined font data that is stored in the printer's associated data memory. The printer's associated data memory includes read only memory (ROM) or some type of printer cartridge or the like. Soft fonts are comprised of data that may be communicated to the printer's buffer memory such as a random access memory (RAM) or the like. The soft fonts are thus predefined in the input computer and are downloaded to the printer when the print job is requested. When a document is to be printed data defining the document ms communicated from the attached computer to the printer. This data defines which characters to print and where to print them on the page to be printed. The printer retrieves the definition of the character from its memory and directs a printing mechanism to print the characters in accordance with the character data received from the computer. Since the characters are predefined, it is not necessary to graphically generate each one when printing the document. Thus, printing in accordance with this process can proceed in a relatively expeditious manner. However, such process, although suited for the printing of textual material, is not appropriate for the presentation of graphic material.
Present high speed non-scalable printing machines, such as the XEROX model 4135, are widely used for printing documents containing text characters at very high rates, on the order of 135 pages per minute. This type of printer, however, is not suitable for representing large amounts of graphical material. It would therefore be desirable to provide a method for enabling graphic data to be generated on such high speed printers at a rapid rate on the order of that associated with printing textual material. In the case of investment reports, such as those relating to pension plans for large companies, it is desirable for each report to contain a customized graphical representation of an employee's investment portfolio, typically in a pie-chart or the like. When printing many copies of these reports even the simple graphical arrangement of a pie chart can require much more printing time than that required to print the textual portions of the document. Thus, it is not commercially feasible to print out high speed documents containing text and graphical materials on a non-scalable printing machine.